A printing plate material for the CTP system, which is inexpensive, can be easily handled, and has a printing ability comparable with that of a PS plate, is required accompanied with the digitization of printing data. Recently, printing plate materials applied to various CTP systems, employing infrared laser has been proposed.
Of these CTP systems, there is a CTP system called a wet type CTP in which solubility of the image formation layer of a printing plate material is varied by imagewise exposure, followed by development with a liquid developer to form an image. However, this system has various problems, in that an exclusive alkali developer is required as in conventional PS plates, developability of developer used varies due to the developer conditions such as temperature or fatigue degree of the developer, image reproduction is not obtained, or operation under room light is restricted.
On the other hand, a printing plate material for so-called a dry CTP system, which does not require special development (including development on press), has been developed. The dry CTP system has been noticed, since it can be applied to a printing press for a direct imaging (DI) system, in which an image is formed directly on a printing plate material mounted on the printing press to obtain a printing plate, and printing is carried out employing the printing plate.
As a printing plate material for the dry CTP system, there is an ablation type printing plate material, for example, one which is disclosed in for example, Japanese Patent O.P.I. Publication Nos. 8-507727, 6-186750, 6-199064, 7-314934, 10-58636 and 10-244773.
These references disclose a printing plate material comprising a substrate and a hydrophilic layer or a lipophilic layer as an outermost layer. In the printing plate material having a hydrophilic layer as an outermost layer, the hydrophilic layer is imagewise exposed to imagewise ablate the hydrophilic layer, whereby the lipophilic layer is exposed to form image portions. However, there are problems that sensitivity is low, which requires great energy for ablation, and resolution is low on account of physical destruction of the hydrophilic layer, which results in lowering of dot quality.
Further, there is problem in which the interior of the exposing apparatus is contaminated by scattered matters caused by ablation of the surface layer. Therefore, the apparatus requires equipment of a special suction device or another cleaning device. In order to prevent the contamination during exposure, a printing plate material may be covered with a cover sheet. Further, a means (for example, a wipe-off device or a rinsing device) for removing scattered matter remaining on the printing plate material surface layer is required. The ablation method does not necessarily provide a complete dry system.
In the ablation type CTP system, a printing plate material has been sought which has good performance and excellent handling property.
Further, a printing plate material has been sought which is capable of forming an image without producing ablated matter and without any special development or cleaning treatment. There is one capable of being developed with dampening water (development on press) disclosed in, for example, Japanese Patent Nos. 2938397 and 2938398, which comprises an image formation layer containing thermoplastic polymer particles and a water soluble binder.
However, such a printing plate material, when a grained aluminum plate is used as a hydrophilic substrate, is required to contain a light heat conversion material (generally colored) in the image formation layer, and may contaminate a printing press in development on press.
In order to prevent such a contamination of a printing press due to development on press, a printing plate material, which comprises a hydrophilic support comprising a substrate and provided thereon, a hydrophilic layer containing a light heat conversion material, has been sought. The use of such a hydrophilic support makes it possible to remove a light heat conversion material from an image formation layer and to optionally select a substrate such as a PET (polyethylene terephthalate) film or an aluminum plate. It is difficult to give an excellent performance identical to the grained aluminum plate to the hydrophilic layer. Although many studies on a hydrophilic layer have been made, a printing plate material providing sufficient printing performance has not yet been obtained.
A hydrophilic layer containing a hydrophilic light heat conversion material is disclosed, for example in Japanese Patent O.P.I. Publication No. 2000-355178. In this publication, no reference is made to components other than the light heat conversion material, and there is description in the examples in which when printing is carried out employing dampening water containing IPA (isopropyl alcohol), no background contamination is not produced. The hydrophilic layer disclosed in the examples cannot be applied to a printing method employing an IP free dampening water which is sought for improvement of working environment.
Further, such a hydrophilic layer, which is formed by a coating method, is poor in layer strength as compared with a grained aluminum plate. Although the hydrophilic layer, when printing is carried out employing a coat paper sheet, can provide good prints, it has problems in that when printing is carried out employing an uncoated paper sheet, spotted layer exfoliation at non-image portions of the hydrophilic layer occurs due to paper powder, resulting in extreme lowering of printing durability. In order to enhance the hydrophilic layer and minimize a layer exfoliation, a hydrophilic layer has been proposed which contains an organic binder compound or a crosslinking agent. However, this hydrophilic layer has drawback in that background contamination is likely to be produced. As is described above, it is difficult to provide both good printing performance and high printing durability to uncoated paper to be printed.